scripts: blender_wrl_to_x3d: Delete that stupid cube

Blender puts a default cube in place in the default scene, but we don't
want this exported in our X3D models, so we need to delete it before
doing anything else.
3d_models: Mass update of X3D models

Original conversion using blender included the default blender cube,
which was unintended. This commit fixes that.

NOTE
Colorization for X3D models still needs to be revisited since colors
were originally tailored for render using KiCad's old rendering engine.